In This Presentation TYPES OF MAINTENANCE REACTIVE MAINTENANCE PREVENTIVE MAINTENACE PREDICTIVE MAINTENANCE PROACTIVE MAINTENANCE RELIABILITY CENTRED MAINTENANCE(RCM) RELIABILITY CENTRED MAINTENANCE HIERACHY OBJECTIVE OF RCM RCM PRINCIPLES RCM –Cost of maintenance and repair RCM AND FAILURE ANALYSIS FAILURE MODES AND EFFECTS ANALYSIS(FMEA) INTERPRETING THE FMEA Risk Priority Number (RPN) or Criticality/Severity Categories HOW TO INITIATE RCM
REACTIVE MAINTENANCE Reactive Maintenance is also referred to as breakdown, repair, fix-when-fail, or run-to- failure (RTF) maintenance. When applying this maintenance technique, maintenance, equipment repair, or replacement occurs only when the deterioration in the condition of the equipment causes a functional failure.
PREVENTIVE MAINTENACE One of the underlying assumptions of maintenance theory has always been that there is a fundamental cause-and-effect relationship between scheduled maintenance and operating reliability. This assumption was based on the intuitive belief that because mechanical parts wear out. For example, a common practice has been to replace or renew bearings after a specified number of operating hours, assuming that bearing failure rate increases with time in service.
PREDICTIVE MAINTENANCE Predictive maintenance or condition monitoring, uses primarily non intrusive testing techniques, visual inspection, and performance data to assess machinery condition. Condition monitoring replaces arbitrarily timed maintenance tasks with maintenance that is scheduled only when warranted by equipment condition. Continuing analysis of equipment condition-monitoring data allows planning and scheduling of maintenance or repairs in advance of catastrophic and functional failure.
PROACTIVE MAINTENANCE Proactive is the opposite of Reactive. Proactive maintenance is an activity performed to detect and correct causes of failure i.e. actions taken to correct conditions that could lead to material degradation. Instead of investigating material and performance degradation factors to determine the extent of incipient and impending failure conditions, proactive maintenance concentrates on identifying and correcting abnormal causes of failure that create unstable operating conditions.
HISTORICAL EVOLUTION OF RELIABILITY CENTRED MAINTENACE In the case of aircraft it was also commonly assumed that all reliability problems were directly related to operating safety. Over the years, However, it was found that many types of failures could not be prevented no matter how intensive the maintenance activities.
INTERODUCTION TORELIABILITY CENTRED MAINTENANCE While many industrial organizations were expanding PM efforts to nearly all other assets, the airline industry, led by the efforts of Nowlan and Heap, took a different approach and developed a maintenance process based on system functions, consequence of failure, and failure modes. Their work led to the development of Reliability- Centered Maintenance, first published in 1978.
RELIABILITY BASED MAINTENANCE Reliability-Centered Maintenance (RCM)- integrates Preventive Maintenance (PM), Predictive maintenance and Proactive Maintenance to increase the probability that a machine or component will function in the required manner over its design life-cycle with a minimum amount of maintenance and downtime.
RELIABILITY CENTRED MAINTENANCE HIERACHY RELIABILITY CENTRED MAINTENANCE REACTIVE PROACTIVE MAINTENANCE MAINTENANCE *Small item *Root cause failure analysis *Non critical PREVENTIVE PREDICTVE *Age exploration *Unlikely to fail MAINTENANCE MAINTENANCE *FMEA *Redundant *Subject to wear out *Not subject to wear out *Known failure pattern *Random failure *Consumable *PM induced failure
OBJECTIVE OF RCM To ensure realization of the inherent safety and reliability levels of the equipment. To restore the equipment to these inherent levels when deterioration occurs. To obtain the information necessary for design improvement of those items where their inherent reliability proves to be inadequate. To accomplish these goals at a minimum total cost, including maintenance costs, support costs, and economic consequences of operational failures.
RCM PRINCIPLES Reliability-Centered: RCM treats failure statistics in an actuarial manner. The relationship between operating age and the failures experienced is important. RCM is not overly concerned with simple failure rate; it seeks to know the conditional probability of failure at specific ages .
RCM PRINCIPLES Acknowledges Design Limitations: The objective of RCM is to maintain the inherent reliability of the equipment design, recognizing that changes in inherent reliability are the province of design rather than maintenance. Maintenance can only achieve and maintain the level of reliability for equipment which is provided for by design. RCM recognizes that maintenance feedback can improve on the original design.
RCM PRINCIPLES -DESIGN IMPROVEMENTS THROUGH MAINTENANCE FEEDBACK Life extension
RCM PRINCIPLES Function-Oriented: RCM seeks to preserve system or equipment function, not just operability for operabilitys sake. Redundancy of function through redundant equipment improves functional reliability but EXAMPLE-REDUNDANT increases life-cycle cost UPS DESIGN in terms of procurement and operating costs.
RCM PRINCIPLES Tasks Must Be Applicable: Tasks must address the failure mode and consider the failure mode characteristics. System-Focused: RCM is more concerned with in maintaining system function than individual component function.
RCM PRINCIPLES Logic Tree to Screen Maintenance Tasks: This provides a consistent approach to the maintenance of all equipment.
RCM PRINCIPLES Safety, Security, and Economics: Safety and security must be ensured at any cost; life- cycle cost-effectiveness is a tertiary criterion. Failure as Any Unsatisfactory Condition: Failure may be either a loss of function (operation ceases) or a loss of acceptable quality (operation continues).
RCM ANALYSIS RCM analysis carefully considers the following questions: What does the system or equipment do; what are its functions? What functional failures are likely to occur? What are the likely consequences of these functional failures? What can be done to reduce the probability of the failure, identify the onset of failure, or reduce the consequences of the failure?
BENEFIT OF RCM To avoid loss of life, property damage, and environmental harm, The cost of repair decreases as failures are prevented . RCM places great emphasis on improving equipment reliability. A principal advantage of RCM is that it obtains the maximum use from equipment. With RCM, equipment replacement is based on actual equipment condition rather than a predetermined, generic length of life.
RELIABILITY CENTRED MAINTENANCE Advantages Efficient. Increased system reliability. Lowered costs due to no unnecessary maintenance. Minimized overhauls. Reduced sudden equipment failures. Maintenance focused on critical components. Incorporates root cause analysis. Disadvantages Significant initial costs for training, and equipment. Savings potential not readily seen by management.
RCM –Cost of maintenance and repair Due to the initial investment required for obtaining the technological tools, training, and equipment condition baselines, a new RCM Program typically results in an increase in maintenance costs. This increase is relatively short-lived, averaging two to three years. The cost of repair decreases as failures are prevented and preventive maintenance tasks are replaced by condition monitoring. The net effect is a reduction of both repair and total maintenance costs. Often energy savings are also realized from the use of condition monitoring techniques.
COST OF MAINTENANCE AND REPAIR (NASA) Initial cost saving
Cost of Maintenance Programs (Piotrowski 2001)(in $per horse power per year)18 $181614 $1312 REACTIVE10 $9 PREVENTIVE 8 $6 PREDICTIVE 6 RCM 4 2 0
RCM AND FAILURE ANALYSIS Failure is the cessation of proper function or performance. RCM examines failure at several levels: the system level, subsystem level, component level, and the parts level. The goal of an effective maintenance organization is to provide the required system performance at the lowest cost. This means that the maintenance approach must be based upon a clear understanding of failure at each of the system levels.
CAUSES OF FAILURE The cause of a failure mode is a deficiency that results in the failure mode. A failure mode can be caused by one or more of the individual components or by: • Inadequate component design • Improper installation or maintenance • Improper selection of component parts • Improper use of processes • Inadequate control procedures It is imperative that the focus in performing the FMEA should be to identify all potential failure .
FAILURE MODES AND EFFECTS ANALYSIS Failure Modes and Effects Analysis (FMEA) is applied to each system, subsystem, and component identified in the boundary definition. For every function identified, there can be multiple failure modes. The FMEA addresses each system function, all possible failures, and the dominant failure modes associated with each failure. The FMEA then examines the consequences of failure to determine what effect failure has on operation, on the system, and on the machine.
INTERPRETING THE FMEA The FMEA is done to identify and/or eliminate deficiencies and therefore eliminate or at least minimize failure rate. The traditional way to interpret the results of the FMEA is to calculate the Risk Prioritization Number (RPN) or Criticality/Severity Categories.
Risk Priority Number (RPN)or Criticality/Severity Categories This number is the product of severity, frequency and detection. The RPN defines the priority of the failure. On its own the RPNs has no value or meaning. It is only used to rank (define) the potential deficiencies. A goal of FMEA is to reduce the RPN or Criticality/Severity Categories The severity can be reduced through a change in design, configuration and/or through a change in how it is operated
Risk Priority Number (RPN)or Criticality/Severity CategoriesEFFECT RANKING CRITERIAnone 1 Results in no loss of function, reliability , safety margin, health, environment or mission.Very slight 2 Very slight reduction in performance and integrity. Repair to failure can be accomplished during trouble callslight 3 Slight reduction in performance .repair to failure may be longer than trouble call .Minor 4 Minor reduction in current performance. some portion of mission may need to be rework or process delay.moderate 5 Moderate disruption to facility function .100% of mission may need to be reworked or process delaysignificant 6 Significant disruption to facility function .some portion of mission is lost. Delay in restoring function.major 7 High disruption to facility function .some portion of mission is lost. Delay in restoring function.extreme 8 High disruption to facility function .significant delay in restoring function.serious 9 Potential safety ,health or environment issue .failure will occur with warning.hazardous 10 Potential safety, health or environment issue .failure will occur without warning.
HOW TO INITIATE RCM 1.Develop a Master equipment list identifying the equipment in your facility. 2.Prioritize the listed components based on importance or criticality to operation, process .Assign components into logical groupings. 3.Types of Maintenance Programs 4.Determine the type and number of maintenance activities required and periodicity using: a. Manufacturer technical manuals . b. Machinery history . c. Root cause analysis findings - Why did it fail? d. Good engineering judgment . 5.Assess the size of maintenance staff & Identify tasks that may be performed by operations maintenance personnel. 6.Analyze equipment failure modes and impacts on components and systems. 7.Identify effective maintenance tasks or mitigation strategies.
Transition to RCM -A case study Some plants are turning to reliability-centered maintenance (RCM) ,However, appropriate use of RCM creates increased demands for testing (e.g., non-destructive evaluation), data collection, and analysis. The lack of such data collection and analysis appears to have been a problem in the electricity distribution outages in Chicago in summer 1999. In reviewing those outages, the Department of Energy Power Outage Study Team (2000) USA, noted that : “Many fixed, periodic, substation maintenance programs had been scaled back or discontinued in transition to a „reliability-centered maintenance‟ philosophy. However, the collection of data and measurements necessary for successful reliability-centered maintenance was not fully in place.” As a result, “the ability to predict possible component failures from the inspections that were performed and data that were collected was limited.”
Principles of Maintainability Design Great maintenance procedures cannot overcome poor equipment design. Special tools are rarely available when maintainers need them, so design all maintenance tasks to eliminate the need for special tools.